Traditionally high speed printing has been performed using offset printing systems. In a typical high speed offset printing system a continuous web of paper is supplied from a large reel and the paper is fed through successive print stations. Each print station has an impression cylinder that is outfitted with one or more patterned printing plates and applies one type of ink to the receiver according to the pattern on the printing plates.
More recently, high-speed plateless printing systems have been introduced that form patterns of one or more colorants or other donor materials on a paper without the use of printing plates. In one example, this is done using digitally controlled print heads that direct fine drops of ink across an air gap and onto a paper. In another example, this is done by digitally creating toner images and transferring these toner images onto a paper. High speed plateless printing systems such as the Kodak Prosper Press Solutions including the Prosper 1000 and 5000 printing systems, the Kodak Versamark V-Series Printing Systems including the VL Series of printing systems, the VX5000 printing systems and VT5000 printing systems and Kodak Nexpress 2100, 2500 and 3000 printing systems all sold by Eastman Kodak Company, Rochester, N.Y., USA, have demonstrated the ability to provide high quality prints at commercial rates of production.
Plateless printers such as those described above also offer greater flexibility, adaptability, and efficiency than can be provided by conventional plate based offset printing. For example, plateless printing systems have the ability to provide a greater range of print sizes, print shapes, and print aspect ratios than plate based systems. Further, plateless printing systems can vary what is printed on a page by page basis whereas plate based offset printers print the same content on every printed page that is printed using a printing plate. The printed output of both offset and plateless printing systems is typically processed to form into finished articles, such as newspapers, pamphlets and books using conventional equipment. However, much of the commercially available finishing equipment equipment is adapted for use with conventional offset presses. Accordingly, the printed output of plateless printing systems is typically made to conform to the characteristics of the printed output of offset printers to enable such printed output to be processed using such finishing equipment. Thus, many opportunities for unique and improved output options made possible through plateless printing are sacrificed to enable compatibility.
For example, one of the more desirable printed products is a bound combination of printed pages such as are used in making a book or booklet. A conventional process for forming such a book or booklet is by offset printing a large sheet within the printed large sheet that is about the same size as a printing plate with printed pages that are arranged within the printed so that the large sheet can be folded to form smaller sheets with the printed pages in a desired order. The folded sheets are bound together and the folds are trimmed as necessary to allow pages to be turned. The folded, bound, and trimmed output generated from a single printed sheet is conventionally known as a signature. A signature can be used for many purposes. For example, a single signature can form a small booklet or pamphlet with a limited number of pages or a signature can be bound together with other signatures to provide a thicker publication such as a book. A wide variety of other foldable output products are known and various examples of folding processes that can be used for folding a multi-page printed sheet into a signature into a signature or other multi-page printed output, are illustrated in a worldwide web page entitled: “Folding Digital Print Projects”, published by Tecstra Systems, at http://digitalprintingtips.com/printing-tips-t-30-540/folding-digital-pintprojects.asp.
FIGS. 1 and 2A-2C illustrate a widely used method for using a printed paper generated by a continuous web printing system 200 to prepare a signature 240. Referring now to FIG. 1, printing system 200 prints on a paper 202 that takes the form of a web 204 that is substantially continuous along a length of paper 202 and that is stored as a roll 206 wound on a core 208. During printing, paper 202 is fed lengthwise into system 200 from roll 206 and advanced along a transport path T through one or more printing subsystems shown here as printing subsystems 212a, 212b, 212c, and 212d such that a printed paper 214 is formed having printed areas 210 on both a first side 214a and a second side 214b. 
As is also shown in FIG. 1, printing system 200 includes a finishing subsystem 216 with a cutter (not shown) of conventional design that separates a printed paper 214 from web 204 of paper 202 and a series of folders 218a, 218b, and 218c creates a series of folds in printed paper 214. In this example, first folder 218a forms a first fold F1 in printed paper 214 along the length of printed paper 214, second folder 218b forms a second fold F2 is across a width of the first folded paper 214 and third folder 218c forms third fold F3 across a width of the first folded and second folded paper 214. The printed and folded paper 214 is then bound proximate to third fold F3 and trimmed to form a form signature 214 with pages that can be turned about the binding at the third fold F3.
FIGS. 2A-2C illustrate various aspects of the conventional signature making process of FIG. 1 in greater detail. FIG. 2A provides an example of a paper 214 printed on first side 214a and on second side 214b. In this example, page prints 1-16 represent portions of printed paper 214 that are assigned to receive any printing that is to be presented on pages 1-16 of the signature 240 after folding. Accordingly, page prints 1-16 are arranged as required to enable a 16 page signature to be made by folding printed paper 214 according to the prior art method for making a signature. In FIG. 2A, respective locations and orientations for each of the 16 page prints are shown as boxes numbered 1-16.
FIG. 2B illustrates use of the conventional method to convert a printed paper 214 of FIG. 2A into a signature 240 having pages 1-16 arranged in a sequential fashion. At the first fold F1, printed paper 214 is folded across a length to yield two equal sized sheets 220 and 222 jointed at first fold F1. At the second fold F2, sheets 220 and 222 are folded together across a width of sheets 220 and 222 to yield four equal sized folded sheets 225, 227, 229 and 231 joined at first fold F1 with sheets 225 and 227 also joined at second fold F2 in sheet 220 and with sheets 229 and 231 joined at second fold F2 in sheet 222. During a third fold F3, sheets 225, 227, 229 and 231 are then folded across a width and to yield eight two sided sheets shown here as sheets 233, 235, 237, 239, 241, 243, 245, 247, and 249 with printed pages 1-16 sequentially arranged on respective front and back sides thereof. All of these sheets are joined at first fold F1 with sheets 243 and 245 joined at second fold F2 and with sheets 247 and 249 joined at second fold F2.
As is also shown in FIG. 2B, in the method of FIGS. 1 and 2A-2C, folds F2 and F3 involve nested folding of two or more adjacent, parallel and equally sized sheets. As is shown in FIG. 2C, when two adjacent and equally sized sheets 220 and 222 are folded across a width at fold F2, the folded sheet that is closest to fold location F2, shown here as sheet 220, has a first fold radius 232 and fold F2 and a first fold length 234 defined by a length of sheet 220 that is used in allowing sheet 220 to fold. In comparison, a second folded sheet that is further from second fold F2, shown here as sheet 222, will be folded about first sheet 220 in order to make second fold F2 and will necessarily have a second fold radius 242 that is greater than first fold radius 232 and therefore will also have a second fold length 244 that is longer than a first fold length 234. Thus, where, as here, first sheet 220 and second sheet 222 have the same length, the shorter first fold length 234 of first sheet 220 will cause folded sheets 225 and 227 to extend from second fold F2 to a greater extent than sheets 229 and 231 will extend from second fold F2. Therefore, an uneven edge is formed opposite second fold F2 and the lateral location of printed pages can be in different places and can appear to shift relative to second fold F2 from page to page. These outcomes can be seen as objectionable in many printed products.
The page extension variations caused by such multi-page folding are commonly known as creep. The extent of creep in a signature 240 can vary depending on characteristics such as paper thickness, printing type, page stiffness, humidity, temperature, and other factors.
It will also be appreciated that creep related page extension variations of the type shown in FIG. 2C also arise at a face of signature 240 that is opposite to third fold F3. However, the extent of such creep induced variations at the face of signature 240 that is opposite from third fold F3 is typically more pronounced than the extent that exists at second fold F2. In one respect, this is because four equal sized sheets are folded about third fold F3 thus the difference between the fold length of an outermost folded sheet at third fold F3 and the fold length of an inner most folded sheet at third fold, F3 is greater than the difference between fold lengths 234 and 244 of sheets 220 and 222 folded at second fold F2.
In another respect, this can be because the fold at F3 is a fold of sheets that may exhibit creep formed at the second fold F2, thus the extent of the variations in the extent to which pages created at third fold F3 extend from third fold F3 reflect not only those induced at third fold F3, but also those induced at second fold F2, compounding the extent of creep related variations at the face opposite third fold F3.
The conventional method for forming a signature provides a signature 240 that has a number of limitations. As is illustrated in FIG. 2B, the first limitation is that all pages in signature 240 are joined by first fold F1 and two more page pairs are joined at second fold F2. These pages must be separated to provide eight independently turnable pages. Further, a folded signature 240 of the prior art has a first face 236 along which all pages of signature 240 are joined to at least one other page by the first fold F1 and a second face 238 opposite from the third fold F3 along which certain pages are joined by second folds F2.
One way to address these problems is to trim signature 240 along first face 236 to remove first folds F1 from signature 240 and to trim signature 240 along second face 238 to remove second folds F2 from signature 240. Such trimming can also be used to form an edge opposite third fold F3 with pages that extend from fold F3 by a common distance. However, it will be appreciated that first face 236 and second face 238 are arranged along orthogonal edges of signature 240. Thus a single axis trimming tool cannot be used for this purpose without rotating either the signature 240 or the trimming tool.
Alternatively, two trimming tools can be used with one trimming tool arranged to trim signature 240 along first face 236 and another arranged to trim signature 240 along second face 238. However, this approach is more expensive and in certain circumstances may require cutting across a direction of movement of signature 240 which can interrupt finishing work flow.
Further, conventional signature forming methods make signatures using half sheet folding processes. Thus, the number of pages that can be in a signature that is made in this fashion is a fraction of the number of folds, such that the number of pages P=2N where N is the number of half sheet folds and a conventionally made signature typically provides 4, 8, 16, or 32 pages. Thus, to prepare a finished output that does not require one of these numbers of pages, some modification of the conventional sequence is required, for example, to prepare a 24 page product, a 32-page signature can be formed, however this includes eight unnecessary pages. These unnecessary pages can be removed from the signature however; this wastes paper and adds time and labor expense.
Another limitation of conventional signature making methods is that they severely restrict page sizes and aspect ratios by relying on half sheet folding processes. For example, the folding limitations and tolerances required by trimming and other operations, can make it difficult to print and finish small books, such as novelty books, flip books, marketing materials, photo albums, and photo books consumer photographs at small or standard sizes, such as 4×6 inches, for example.
It will be appreciated from the above that conventional methods and apparatuses for signature preparation do not take advantage of new capabilities provided by plateless printing systems. This includes the capability to print jobs of various page lengths, and various pages sizes, and to switch from one job to the next without interruption of the high speed plateless printing process.
Thus, it can be seen that in order to meet the needs of a dynamic printing market, there is a need for printing systems and finishing systems and methods that enable the formation of signatures in a manner that efficiently produces signatures while also leveraging the increased flexibility and advanced capabilities of plateless printing systems.